The invention relates to a sealing ring of the type having a support ring and a polymeric sealing disk which has a retaining segment and a sealing segment. The retaining segment is connected to the support ring and the sealing segment is curved in the direction of a space to be sealed off and sealingly surrounds the shaft along a peripheral side of the sealing segment with a degree of radial prestressing. The sealing segment on the side facing the shaft has a first surface profiling, the first surface profiling on the side facing the space to be sealed off being formed by at least one recirculating element, and at least one dust lip being arranged on the side of the recirculating element facing away from the space to be sealed off.
A sealing ring of this type is described in the German Laid-Open Print 33 16 063. The sealing ring is provided for a machine part that executes rotational motions and is composed of a support ring that is connected in a liquid-tight manner to a sealing disk made of PTFE. The sealing disk is trumpet-shaped and faces the space to be sealed off, and, on the side facing the shaft to be sealed off, it has recirculating elements that act in a hydrodynamic manner. The trumpet-shaped sealing disk is provided with at least two recirculating elements of different profile depths and/or gradients, the recirculating elements being aligned in the same direction and penetrating each other.
The present invention is directed to the refinement of a sealing ring of the type noted above so that the sealing ring has improved static sealing when the shaft to be sealed is at rest.
Between the recirculating elements and the dust lip an annular, a self-contained sealing bead is arranged that sealingly encloses the shaft on its peripheral side.
In a configuration of this type, it is advantageous that the sealing segment of the sealing disk on the side facing the shaft to be sealed has three functional areas that are variously configured, each of the functional areas being responsible for achieving only one objective. The first surface profiling causes a recirculation of the medium to be sealed in the direction of the space to be sealed off. The sealing bead surrounds and encloses within itself the shaft to be sealed and in this manner, when the shaft is at rest, prevents leakage of the medium to be sealed in the direction of the dust lip, i.e., in the direction of the ambient environment. The dust lip effects a protection of the sealing bead and of the recirculating element from abrasive impurities from the ambient environment. The dust lip surrounds the surface of the shaft to be sealed preferably at a very small radial clearance in the range of a maximum of 0.5 mm or in special cases even being able to have contact with the shaft. The dust lip therefore has no wear and maintains good working properties throughout a long service life.
The recirculating element preferably is configured so as to be spiral-shaped and, viewed from the longitudinal section, has saw-tooth-shaped first recesses, which are placed so as to be adjoining and to have axial distance in relation to each other, the first boundary surface of each recess facing the space to be sealed forming a smaller angle with the surface of the shaft to be sealed than the second boundary surface facing away from the space to be sealed. The saw-tooth-shaped profile of the first surface profiling has the advantage that during the normal use of the radial shaft sealing ring, the medium to be sealed off is recirculated very well in the direction of the space to be sealed. As a result of the significantly larger volume of the saw-tooth-shaped recesses in comparison to indentations (i.e., notches) the recesses are less sensitive to oil carbons.
On the side of the recirculating element facing away from the shaft, it is preferable that a second surface profiling be arranged which, in the longitudinal section, is formed by second recesses running along the peripheral side, open on the side facing away from the shaft, and essentially U-shaped, the recesses being placed so as to be adjoining and to have axial distance with respect to each other. The saw-tooth-shaped recesses on the side of the sealing disk facing the shaft and the U-shaped recesses on the side of the sealing disk facing away from the shaft result in the sealing disk being very flexible in the radial direction and being able to follow the movements of the shaft to be sealed even in the event of radial deviations (i.e., run-outs). In addition, the U-shaped recesses, in connection with the saw-tooth-shaped recesses, result in a very large surface, which is well-suited to quickly remove from the sealing disk the frictional heat that arises.
The sealing disk is preferably composed of PTFE. In this manner, the sealing disk is resistant to most of the media to be sealed off. In addition, PTFE has good temperature resistance, as well as good sliding behavior. The sealing disk made of PTFE is virtually wear free, since after a certain initial wear, the surface is glazed and as a result becomes very resistant.
For example, injection-moldable copolymerides can be used such as FEP (perfluoroethylene propyl) or PFA (perfluoralcoxy copolymer) or a thermoplastic elastomer. However, the sealing disk can also be made of other materials.
The sealing disk preferably has a thickness of from 0.5 to 1 mm. The working properties are particularly advantageous if the thickness is from 0.6 to 0.75 mm, depending on the diameter of the shaft to be sealed. If the thickness of the sealing disk is less than 0.5 mm, it is disadvantageous that the recesses have to be reduced in their depth and the sealing disk encloses the shaft to be sealed with but a very small prestressing.
On the other hand, if the thickness of the sealing disk is more than 1 mm, it is disadvantageous that the sealing disk contactingly surrounds the shaft with a too great prestressing, leading to very large power losses.
The saw-tooth-shaped and/or U-shaped recesses, in the event the sealing disk is made of PTFE, are preferably impressed into the sealing disk without the removal of any material. In the case of injection-moldable copolymerides, the recesses are applied in the extrusion die. As a result of the fact that the recesses are manufactured so as to avoid machining processing methods, it is advantageous that the sealing disk, even if the shaft to be sealed off has radial deviations, stands up to a very high number of load changes without suffering damage, since the stress concentrations in the area of the recesses are significantly reduced in comparison to machining processing methods.
The saw-tooth-shaped and U-shaped recesses are preferably staggered in relation to each other. As a result of a configuration of this type, on the one hand, the result is an approximately identical material strength along the axial extension of the sealing disk; undesirable concentrations of material, which are disadvantageous from the point of view of production engineering and with a view to good working properties, are avoided by a configuration of this type. On the other hand, the articulated points are located between the saw-tooth-shaped recesses, so that the geometric dimensions of the saw-tooth-shaped recesses substantially are maintained, even if the sealing disk is used to seal shafts that are not round.
The ratio of the radial depth of the U-shaped recesses to the radial depth of the saw-tooth-shaped recesses can be from 1 to 4.5, with 3 being preferable. A ratio of this type provides an excellent balance among the good flexibility of the sealing disk in the radial direction as compensation for radial deviations of the shaft, a good seal of the medium to be sealed over a long service life, and a large surface for cooling the sealing disk and for removing the frictional heat.
The sealing beadxe2x80x94viewed in the longitudinal sectionxe2x80x94can be essentially configured so as to be square. The axial extension between two axially adjoining boundary surfaces preferably corresponds essentially to the axial extension of the sealing bead and to the axial extension of the dust lip. In a configuration of this type, it is advantageous that the axial width of the sealing ring can be kept optimally small.
According to an advantageous embodiment, provision can be made that the retaining segment is connected to the support ring by an intermediate layer made of elastomer material. Bonding the retaining segment to the intermediate layer can occur, for example, through the vulcanization of the two parts to each other. From an economic point of view, it has proven to be beneficial to produce the intermediate layer in the course of an immediate molding process and simultaneously to connect it to the support ring and the sealing disk by vulcanization.
According to a further embodiment, the retaining segment and the support ring can be directly braced on each other using a tensioning element made of a tough material. In this context, it is advantageous that the manufacture of a sealing ring of this type is particularly simple and therefore can be carried out in a cost-effective manner. The support ring and the tensioning element, for example, can each be made of a metallic material. As a result of the only force- and/or form-locking connection of the retaining segment between the support ring and the tensioning element, a separation of the components of the sealing ring is particularly simple after its use. The individual components can each be recycled according to type.
According to a further embodiment, provision is made for a nonwoven-fabric disk in the case of large quantities of dirt in the ambient environment.